Magnetic material



Jan. 14, 1930;

A. F. BANDUR 1,743,089

MAGNETIC MATERIAL Original Filed Dec. 13, 1924 2 Shets-Sheet l 221426 050 mb/o/io/w MAX FLUX Df/YS/T) Bu.

lm/enfor Adda/7 [Ba/74w b7 My Patented Jan. 14, 1930 UNITED STATES PATENT OFFICE ADOLPH FRANCIS BANDUR, OF IBERWYN, ILLINOIS, ASSIGNOR'TO WESTERN ELECTRIG COMPANY, INCORPORATED, OF NEW YORK, N. Y., A CORPORATION OF NEW YORK MAGNETIC MATERIAL Original application filed December 13, 1924, Serial N'o. 755,613. Divided and this application filed April 26, 1928. Serial N0. 273,080. I

This invention relates to magnetic materials, and is a division of my 'copcnding application, Serial No. 755,613, filed December 13, 1924, now Patent No. 1,673,790, dated June 19, 1928.

The principal object of the invention is to secure constancy of operating characteristics of magnetic material usedfin signaling apparatus and for other apparatus employing low field strengths; examples of signaling apparatus being inductive loading, transformers, relays, filter coils, and balancing and wave-shaping networks.

An object of the invention in a different aspect is to reduce, in niagnetic material used in signaling apparatus, variations in those magnetic characteristics the variability of which introduces distortion in the signaling currents. Two such characteristics are permeability and variable flux due to hysteresis.

Another object is to secure relative constancy of the variable operating characteristics in magnetic material used in signaling apparatus and for apparatus employing low field strengths, and at the same time to secure a high value of permeability.

Another object is to obtain in a magnetic material those characteristics which peculiarly adapt it for use as inductive loading material for signaling lines.

- Other objects of the invention will become of the following apparent onconsideration specification.

Wherever magnetic material is subjected to magnetic fields set up by signaling currents,

these currents are distorted because there is no known magnetic materialwhich does not have some characteristics which varies with in the operating range. Such distortion is variously characterized as modulation. Morse flutter, etc., depending upon the conditions under which it is produced. Permeability ordinarily varies with the field strength or with the resultant flux density. Likewise, when fields due to a' complete cycle of alternati ng signaling current are set up, the flux density is diflferent for equal positive and negative values of the field strength because of the hysteresis of the magnetic material. The resistivity may likewise vary somewhat with field strength which introduces variable losses with consequent distort-ion of the signaling current, but this effect is ordinarily small. It is highly desirable to have high resistivity to avoid excessive eddy current losses and also to have high permeability to enable a given inductance to be obtained with a minimum amount of the material.

In British Patent 189,410 is described an invention of G. W. Elmen pertaining to nickel-iron alloys which in many respects are more suitable for inductive loading than iron. Such alloys may contain from 25% to to around 80% or more of nickel, the preferred proportions being nickel 78 and iron 21 7 A heat treatment suitable for obtaining high permeability, low hyster'esis loss and high resistivity is there described.

The present invention is the outgrowth of an extension of the investigation leading to the invention disclosed in the British Patent 189,410. It is based upon the discovery that when nickel-iron alloys containing from 30% to 60% of nickel are given a special. treatment hereinafter described, the permeability becomes relatively constant over a very wide range of low flux densities-the range ordinarily employed in signaling-and, as compared with iron, the permeability is high, the hysteresis loss very low, and the resistivity very high. The material is better than iron in all of these important respects.

Heretofore, aside from the work'of Elm'en, various investigators have independently in vestigated some of the properties of certain nickel-iron alloys falling within the range from 30% to 60% nickel but not at flux densities with which this invention is concorned.-

The treatment of nickel-iron alloys employed to obtain the properties described above may be outlined as follows: The alloy ingot, after casting, is worked by being rolled and occasionally annealed as found necessary until thin sheets or strips about .002 inch thick are obtained. This process produces a certain moderate degree of hardness in the metal. It is then subjected to a temperature lower than that which would ordinarilybe employed to anneal it and the heat is applied for a obtained within limits by simultaneously increasing one of these factors and decreasing the other. The proper values of temperature and time may be determined by trial in each case. The rate of cooling is preferably more rapid than that ordinarily employed in annealing but has no critical value. Cooling in air at ordinary room temperature is satisfactory. Theprocess of subjecting a material, as just described, to a temperature and for a time insufiicient to secure maximum softness is herein characterized as partially annealing.

in the alloy just mentioned containing 36% of nickel when treated as described, permeability will lie in'the range from 125 to 1000 and the variation of permeability over a range of flux densities from 0 to 100 c. g. s. units is from 2% to 5%. The hysteresis loss at a maximum flux density of 8 c. g. s. units may be as low as 1.5-109ergs. per cycle per em being about l/loth that of hard drawn iron Wire. The resistivity is about 80 microhms per cm. i

Inductive loading of signaling lines is a suitable use of magnetic material to serve as an illustration of the uses and manner of preparation of the new material, and has therefore been chosen tor that purpose in the following specification. I

Heretofore the material which has been generally used for loading telephone lines is iron, the most suitable form being specially prepared compressed iron dust. Another form is that in which the core is a coil of fine iron Wire. Such loading coils are described, for example, in an article by Buckner Speed and G. W. Elmen, entitled lllagnetic prop erties of compressed powdered iron, Journal of the A. l. E. E, July, 1921. 1

In the construction ofloading coils for telephone lines in which the cores are of iron wire, it has been found possible to obtain a semi-hard drawn wire which has an initial permeability approximately 125, the perineability varying by not more than 2% or 3% over a range of flux densities from 0 to 30 c. g. s. units. Its hysteresis loss is 2.2510 ergs. per cycle per cm at amaxir'numhux density of 8 c. g. s. units, and its resistivity is 9 microhms per cm".

In the standard design of loading coil, the magnetizing force corresponding to a telephone current of five niilliamperes, is of the order of .05 gauss. At a permeability of 100 the corresponding flux density is 5 c. g. s.

units. Ordinarily, however, loading must be designed to serve either'near the terminals oi lines or cables where the currents are large or at m1d-lme where the currents have been pose.

misuse reduced by attenuation. In many installations, moreover, telephone and telegraph currents are composited so that the flux in the coils a-tany given point on the line varies over a wide range. In many other uses of magnetizing material designed to operate at flux densities up to 100 c. g. s. units, the flux varies over a large part of this range, as for example in transformers employed to interconnect stages of amplifiers in public address systems and in filter coils for similar systems.

Referring to the accompanying drawings,

Fig. l is a vertical sectional View of a loading coil for loading signaling conductors in which the core of the coil consists of laminations of the improved magnetic material of this invention;

Fig. 2 is a curve showing the variation of permeability of the new magnetic material over a range of flux densities from 0 to 100 c. g. s, units, compared to the grade of iron having the greatest attainable constancy of permeability over this range;

Fig. 3 is a representative curve showing the initial permeability that will be secured in one'form of the improved magnetic ma terial for certain definite heat treatingtemperatures 4: is a representative curveshowing the magnitude of the hysteresis loss thatmay be secured'in a piece of the new magnetic material after being subjected to the several temperatures of heat treatment shown on the graph; and

Fig. 5 shows the percentage change in permeability that occurs when the maximum flux density is changed from 0 to 100 c. g.

units for the improved alloy after having been subjected to the different heat treatments indicated on the graph.

in preparing the material for use the core of a loading coil, nickel and iron in the proportion, for example, of about 36% nickel and the balance of iron are fused in an induction or are furnace. Pure commercial grades of these two metals are suitable for this pur- The molten alloy is poured into an ingot mold and allowed to solidify. The ingot is then subjected to repeated hot rolling operations followed by cold rolling operations by which it is reduced in thickness and correspondingly elongated to have a final thickness of about .002 inch. The stri is then passed through cutting rolls or disks which trim its edges squarely on both sides to give the strip an exact and uniform width of 1 inch. This tape of niclrel-iron composition is then rolled up to form a ring core as shown in Fig. 1, the adjacent convolutions thereof being suitably insulated from each other. in insulating these adjacent turns of the ring core, good results have been secured by subjecting the tape to an oxidizing process prior to wrapping it into the ring in the manner just described. This oxidizing which process consists in removin all oil and grease from the tape with alcoho and subjecting it to an atmos here of oxygen at a temperature above 400 and below the final heat treating temperature (to be described hereinafter). he duration of this process depends upon the thickness of the oxide coating desired, but good results have been secured by heating the material to the temperature stated for about 15 minutes.

The core is then heat treated for a period of time and to a temperature less than would be required for completely annealing itand is then cooled. For example, it has been found desirable to heat the core to a temperature of approximately 480 C. and maintain it at this temperature for about 15 minutes, the

core then being' allowed to cool. Experiments have indicated that the rate of cooling is not critical and good results have been secured by accelerating .the cooling by placing the core in a cold air blast.

It has been found desirable to impregnate the core after heat treating by immersing-it under partial vacuum in a hot molten insulating compound that solidifies on cooling. The core after immersion is removed from the molten compound and allowed to drain and cool. This provides a rigid and substantial coil. A rosin compound consisting of a mixtureof rosin and rosin oil in ratio of three to one has given good results.

For example, to form a loading coil having an inductance of 28 mil henries and an effecting resistance of less than 3.0 ohms with a 1800 cycle alternating current of .002 amperes flowing through a winding of approximately 285 turns of number 22 copper wire, pound of the strip prepared in the manner heretofore described is rolled into a tight ring core, the interior opening of has a diameter of about 1.37 5 inches, the ends of the coil being held in any suitable manner. 7 4 1 The particular value of permeability desired in the material will vary, depending upon the uses to which the material is to be put, and in order to secureany particular value of permeability which will be constant over a wide range of low flux densities, the temperature during the heat treatment is raised to a definite point. Generally stated, the' higher the permeability desired the higher the temperature to which the heating is carried. 4

Fig. 3 shows the initial permeabilities that willbe secured for a range of heat treating temperatures of a nickel-iron alloyk havlng 37 96 nickel, the heat treatment avmg a duration of 15 minutes. In thls figure, permeabilities are plotted as ordinates and temunderstood that peratures as abscissae, it bein the sha e of the curve will epend somewhat upon t e amount and kind of mechamcal treatments to which the material is subjected in flux density below 100 c. g.

while being worked down to its final dimension. In general the same t pe of curve will be obtained for other perio s of application of the heat treatment, the longer the period the lower the temperature at which the maximum point of the curve will occur. The change thus produced by prolonging the period beyond a few hours is not marked.

Fig. 4 shows the magnitude of the hysteresis loss obtained for a range of heat treating temperatures with a nickel-iron alloy having 37 nickel, the heat treatment in each case having a duration of 15 minutes. This figure shows hysteresis loss ergs per cycle per cm? for amaximumiiux density of 8 c. g. s. units as ordinates. The heat treating temperatures are shown as abscissae.

One of the outstanding characteristics of this improved magnetic material is the small change in permeability. that occurs with changes in flux densities below 100 c. g. s. units. By the method of heat treatment herein described it is possible to secure smaller changes in permeability for given changes s. units than when the material is either unannealed or fully annealed. By referring to Fig. 5 it will be apparent the way in which the method of heat treatment herein described reduces the percentage change in permeability. The

curve of Fig. 5 is representative and may.

shift up or down or laterally depending on the previous history of the material.

In Fig. 2 are curves showin the variations of permeability with flux density for the most suitable grade of iron in comparison with the improved magneticalloy. By reterring to curve A which is representative of the form of iron having the most constant permeability over this range, and to curve B representative of the improved magnetic material in the form of nickel-iron alloy, the

comparative constancy of permeability of the materials over a wide range of low flux densities is'disclosed. Percents of initial permeability are plottedas ordinates and flux densities as abscissae. Curve l3 is-for a nickeliron alloy having 37 70 of nickel.

A coil such as that above described is about one-third or less the volume of the best loading coils designed for the same purpose now in use.

It is obvious that the material just described is adapted forcontinuous'loading of signaling conductors as well as for loading coils. As compared with loading material in which high permeability is developed by heat treatment after the material, in a form suitable for continuous loading, is placed upon the copper conductor, the material of this invention has the advantage that if heat treatment of the loaded conductor becomes desirable or necessary the temperature re-' quired will be relatively low and will not necessitate special precautions to prevent injury to the copper conductor.

This invention is of particular importance in the. loading of lines employing high "frequency, since distortion known as interniodulat-ion is then large when ordinary materials are used.

It is within the scope of this invention to apply to any magnetic material the treatment herein described, modified to suit the particular material and the de ree to which the desired Characteristic or characteristics are to be obtained, for the purpose of obtaining the desirable results herein specified. In another aspect, the invention comprehends the material so treated.

The nickel-iron alloys herein mentioned consist essentially of nickel and iron but other elements'may be'present in small amounts. The range of nickel-iron alloys of this invention from 35% to 38% of nickel is particularly suitable for loading and analo ous urposes, 36% nickel bein perhaps the best, ut the invention is applica le throu hout the entire range from to 60% of nickel and may be usedto advantage for some purposes in the range from 60% to 80% or 90% of nickel.

Zlfhat is claimed is: 1. Magnetic material having a permeability which varies by not more than 2% of its initial permeability over a range of flux densities from 0 to 30 c. s. units and having higher initial permeabfiity than iron having as nearly as possible the same approximation to constancy of permeability over the same range.

2. Magnetic material in accordance with claiml in which the hysteresis efi'ect is like 5 wise lower than for said iron.

3. Magnetic material in accordance with claim 1 in which the resistivity is greater than 7 claim 1 composed principally of nickel and iron, the nickel component being at least- 30% of the whole.

5. Magnetic material in accordance with. claim 1 composed principally of nickel and iron, the nic el component comprising from 30% to 60% of the whole.

6. Magnetic material according to claim 1 composed principally of nickel and iron, the nickel component constituting from to 33% of the whole.

7. Magnetic material composed principally oi? nickel and iron, the nickel component being from 30% to of the whole, having a permeability which varies by not more than 2% ever a range of flux densities of lrom zero to 30 c. g. s. units and havin low hysteresis effect, higher resistivity an higher initial permeability than iron having as nearly as possible the same approximation to constancy of permeability over the same range.

' 8. Magnetio'material ly of nickel and iron, being at least 30% of the nickel-iron content, having an initial permeability greater than 40 and having a permeability over a range of flux densities from 0 to 100 c. g. s. units within a few percent of its initial permeability.

9. Magnetic material according to claim 1 characterized by a variation of permeability of not more than 5% over a range of flux densities from 0 to 100 c. g. s. units.

Magnetic material composed of. a partia y which varies by not more than 2% of its initial permeability over a. range of flux densities from O to 30 c. g. s. units and having higher initial permeability than iron having as nearly as possible the same approximation to constancy of permeability over the same range.

11. Magnetic material composed of a partially annealed alloy having a permeability which varies by not more than 2% of its initial permeability over a range of flux densities from 0 to 30 c. g. s. units, having higher initial permeability than iron having as nearly as possible the same approximation to constancy of permeability over the same range, having a hysteresis efi'ect lower than for said iron, and having a greater resistivity than said iron.

12. Magnetic material composed of a partially annealed alloy of nickel and iron containing from 35 to 38% nickel, having a permeability whichvaries by not more than 2% of its initial permeability over a range of flux densities from 0 to 30 c. g. s. units, and having higher initial permeability than iron having as nearly as possible the same approximation to constancy of permeability over the same range.

13. Magnetic material composed principally of a partially annealed alloy of nickel and composed principalthe nickel component ron in which the nickel component is at least 30% of the nickel-iron compound, having an initial permeability greater than 40, and having a permeability over a range of flux densities from 0 to 100 c. g. 5. units within a few percent of the initial permeability.

14. Magnetic material composed of a partially annealed alloy of nickel and iron containing from to 38% nickel, having a permeability which varies by not more than 2% of its initial permeability over a range of flux densities from 0 to 30 c. g. s. units, having higher initial permeability than iron having as nearly as possible the same approximation to constancy of permeability over the samerange, having a hysteresis effect lower than aforesaid iron, and having a resistivity greator than said iron.

lln witness whereof, I hereunto subscribe my name this 14th day of April A. D., 1928. ADOLPH FRANCIS BANDUR. 

